Because of lightweight properties and ease of recycling, olefin thermoplastic elastomers are widely used for automobile parts, industrially mechanical parts, electrical or electronic parts and building materials, as elastomers of energy-conservation or resource-conservation type, particularly as substitutes for vulcanized rubbers. However, the conventional olefin thermoplastic elastomers generally have a defect of inferior elastomeric properties to the vulcanized rubbers, and improvement of the defect has been eagerly desired.
As improved olefin elastomers which are substitutes for the vulcanized rubbers, completely crosslinked olefin thermoplastic elastomers having high degree of crosslinking (e.g., thermoplastic elastomer described in Japanese Patent Publication No. 18448/1980) have been hitherto proposed. Though the completely crosslinked olefin thermoplastic elastomers are superior to partially crosslinked olefin thermoplastic elastomers in the elastomeric properties, they have problems of moldability and appearance of their molded products, and therefore the use application of the elastomers is specifically limited.
In International Publication WO96/07681, a crosslinked thermoplastic comprising an ethylene/styrene/ethylidene norbornene copolymer and polypropylene is described. However, this crosslinked thermoplastic is not always sufficient in a balance of elastomeric properties, tensile strength, low-temperature properties and surface strength.
The present inventors have earnestly studied to solve such problems as mentioned above. As a result, they have found that a thermoplastic elastomer composition, which is obtained by dynamically heat treating, in the presence of an organic peroxide, a blend comprising a crystalline polyolefin resin and an unsaturated olefin copolymer obtained by random copolymerizing ethylene, an .alpha.-olefin of 3 to 20 carbon atoms and a specific conjugated diene monomer, or a blend further comprising at least one component selected from the group consisting of an ethylene/.alpha.-olefin/nonconjugated polyene copolymer, a peroxide-noncrosslinkable hydrocarbon rubber and a softener in addition to the crystalline polyolefin resin and the unsaturated olefin copolymer, has excellent elastomeric properties and moldability and that a composition comprising this thermoplastic elastomer composition and a crystalline polyolefin resin also has excellent elastomeric properties and moldability. Based on the finding, the present invention has been accomplished.